1. Field of the Invention
The present invention relates to a polymer and a resist composition that can be used as an electronic industrial material such as photoresist, and more particularly, to monomers having multi-ring structure, and a photosensitive polymer and a resist composition obtained from the same.
2. Description of the Related Art
As the manufacture of semiconductor devices becomes complicated and the integration density of semiconductor devices highly increases, there is a need to form a fine pattern. Furthermore, with regard to 1-Gigabit or more semiconductor devices, a pattern size having a design rule of 0.15 xcexcm or less is needed. However, when a conventional photoresist material is exposed with KrF excimer laser (248 nm), there is a limitation in forming such a fine pattern. For this reason, development of a lithography technique using a new exposure light source, ArF excimer laser (193 nm), is under way to be commercially available in the near future. Also, for adoption to the manufacture of semiconductor devices in which formation of patterns of 0.15 xcexcm or less is needed, research into another next-generation technique using F2 excimer laser (157 mn) as a new exposure light source is being extensively conducted.
Whereas research into ArF and F2 excimer laser techniques is being vigorously carried out, existing resist compositions suitable for use in those techniques cause many problems in practical use, compared to conventional KrF resist compositions. Almost all well-known ArF resist compositions contain (meth)acryl-based polymers. Among these polymers, a methacrylate copolymer having an alicyclic protecting group, which is expressed by the formula below: 
This polymer has an adamantyl group, which contributes to enhancing resistance to dry etching, and a lactone group, which improves adhesiveness, in its methacrylate backbone. As a result, the resolution of the resist and the depth of focus has improved. However, resistance to dry etching is still weak, and serious line edge roughness is observed after line patterns are formed from the resist layer.
Another drawback of the polymer having the formula above is that the raw material used to synthesis the polymer is expensive.
As another conventional resist composition, a cycloolefin-maleic anhydride (COMA) alternating polymer having the following formula has been suggested: 
In the production of copolymer, such as a COMA alternating polymer having the formula above, resistance to dry etching is improved and the production cost of raw material is cheap, whereas resolution of the polymer sharply decreases. Also, the copolymer has a glass transition temperature (Tg) of 200xc2x0 C. or higher due to the structural strength of norbornene contained in the backbone, resulting in processing difficulty. In addition, the synthetic polymers have in their backbone the alicyclic group, which shows prominent hydrophobicity, and thus the adhesiveness to neighboring material layers is very poor.
To overcome the-described problems, in recent years, polymers having various structures have been proposed, the polymers exemplified by a copolymer of a COMA system and a monomer units having a (meth)acylate-based backbone: 
Since the copolymer having the above structure has a glass transition temperature (Tg) lower than that of the COMA system, the processing can be easily carried out. Also, since a polarity change occurs to (meth)acrylate monomer units, increased resolution can be achieved. However, according to reports hitherto made, resistance to dry etching has not been enhanced very much. To increase the resistance to dry etching, a bulky protecting group such as an adamantly group, rather than a t-butyl group, is introduced to the above structure. However, the resulting resist still exhibits weak resistance to dry etching or poor patterns.
As the pattern rule becomes finer in the manufacture of semiconductor devices, the aspect ratio is considerably increased, resulting in the collapse of patterns. To avoid this, a lithography technique using ArF excimer lasers may be used. However, in the case of using the lithography technique using ArF excimer lasers, patterns must be formed such that a resist layer is coated on a wafer to a thickness of 4000 A or less. As the thickness of the resist layer is reduced as above, it is necessary to enhance resistance to dry etching.
Another conventional resist composition proposed for enhancing resistance to dry etching includes a polymer having only a norbornene structure in its backbone, represented by the following formula: 
However, in order to obtain the above structure, a catalyst made from a heavy metal such as platinum or nickel is necessary. The heavy metal used as a catalyst during polymerization cannot be completely removed. Thus, the resist composition obtained from the polymer may cause serious contamination due to the heavy metal, making practical use difficult.
To solve the above problems, it is a first object of the present invention to provide monomers used as raw materials for polymers that can be adopted to various light sources including KrF excimer lasers, ArF excimer lasers or F2 excimer lasers in a photolithography process.
It is a second object of the present invention to provide a photosensitive polymer which can be obtained by a simple synthesis method and can provide enhanced resistance to dry etching without contamination due to a heavy metal catalyst.
It is a third object of the present invention to provide a resist composition having enhanced resistance to dry etching and good transmittance, can adopt various light sources including KrF excimer lasers, ArF excimer lasers or F2 excimer lasers in a photolithography process and can provide a good lithographic property of high resolution.
The first object of the present invention can be accormplished by providing a monomer having a structure represented by the following formula: 
wherein R1 is -H or -CH3, R2 and R3 are -H, -OH or an alkyl group having 1-20 carbon atoms. In the monomer according to the present invention, R2 and R3 are preferably selected from a group consisting of alkyl, hydroxyalkyl, alkyloxy, carboxyl, carbonyl, ester, and fluorinated alkyloxy.
Preferably, the monomer has a structure represented by the following formula: 
Also, the monomer preferably has a structure represented by the following formula: 
The monomer may have a structure represented by the following formula: 
Also, the monomer may have a structure represented by the following formula: 
Further, the monomer may have a structure represented by the following formula: 
To achieve the second object, there is provided a photosensitive polymer comprising a monomer unit represented by the following formula: 
wherein R4 and R5 are -H or -CH3, and R6 and R7 are -H1 -OH or an alkyl group containing 1-20 carbon atoms.
In a preferred photosensitive polymer, at least one of R6 and R7 is selected from a group consisting of alkyl, hydroxyalkyl, alkyloxy, carboxyl, carbonyl, ester and fluorinated alkyloxy.
Preferably, the photosensitive polymer has a structure represented by the following formula: 
wherein R8 is an alkyl group having 4-12 carbon atoms, and s is an integer from 0 to 2, preferably 1 to 2.
More preferably, R8 is one of t-butyl, tetrahydropyranyl or a substituted or unsubstituted alicyclic group. Examples of R8 is selected from a group consisting of 1 -methyl-1-cyclohexyl, 1-ethyl-1-cyclohexyl, 2-methyl-2-norbomyl, 2-ethyl-2-norbornyl, 2-methyl-2-isobomyl, 2-ethyl-2-isobomyl, 8-methyl-8-tricyclo[5.2.1.02,6]decanyl, 8-ethyl-8-tricyclo [5.2.1.02,6]decanyl, 2-methyl-2-adamantyl, 2-ethyl-2-adamantyl, 1 -adamantyl-1-methylethyl, 2-methyl-2-fenchyl and 2-ethyl-2-fenchyl.
Also, the photosensitive polymer preferably has a structure represented by the following formula: 
wherein R9 is a C1xcx9cC20 hydrocarbon group.
In the above formula, R9 is selected from a group consisting of methyl, ethyl, a t-butyl and cyclohexyl.
Preferably, the photosensitive polymer has a structure represented by the following formula: 
wherein R10 is selected from a group consisting of methyl, ethyl, t-butyl and cyclohexyl,
Also, the photosensitive polymer preferably has a structure represented by the following formula: 
According to another aspect of the present invention, there is provided a photosensitive polymer having a structure represented by the following formula: 
wherein R4, R5, R11 and R12 are -H or -CH3, R6, R7, R13 and R14 are -H, -OH or alkyl group having 1-30 carbon atoms, at least one of R6, R7, R13 and R14 is an acid-labile group, and m/(m+n) is from about 0.1 to 0.9.
In the photosensitive polymer, at least one of R6, R7, R13 and R14 is preferably selected from a group consisting of alkyl, hydroxyalkyl, alkyloxy, carboxyl, carbonyl, ester and fluorinated alkyloxy.
Preferably, the photosensitive polymer has a structure represented by the following formula: 
wherein R15 is an alkyl group having 4-12 carbon atoms and s is an integer of from 0 to 2, preferably 1 to 2. More preferably, R15 is selected from a group consisting of t-butyl, tetrahydropyranyl, and a substituted or unsubstituted alicyclic hydrocarbon havig 6-12 carbon atoms. Examples of R15 is selected from a group consisting of 1-methyl-l-cyclohexyl, 1-ethyl-l-cyclohexyl, 2-methyl-2-norbomyl, 2-ethyl-2-norbomyl, 2-methyl-2-isobomyl, 2-ethyl-2-isobomyl, 8-methyl-8-tricyclo[5.2.1.02,6]decanyl, 8-ethyl-8-tricyclo[5.2.1.02,6]decanyl, 2-methyl-2-adamantyl, 2-ethyl-2-adamantyl group, 1-adamantyl-1-methylethyl, 2-methyl-2-fenchyl and 2-ethyl-2-fenchyl.
Also, the photosensitive polymer preferably has a structure represented by the following formula: 
wherein R15 is an alkyl group having 4-12 carbon atoms and s is an integer of from 0 to 2, preferably 1 to 2.
The photosensitive polymer preferably has a structure represented by the following formula: 
wherein R16 is a C1xcx9cC20 hydrocarbon group. More preferably, R16 is selected from a group consisting of methyl, ethyl, t-butyl and cyclohexyl.
Also, the photosensitive polymer preferably can have a structure represented by the following formula: 
wherein R17 is an alkyl group having from 1-20 carbon atoms. More preferably, R17 is selected from a group consisting of methyl, ethyl, t-butyl and cyclohexyl.
According to still another aspect of the present invention, there is provided a photosensitive polymer including a polymerized product of (a) at least one monomer unit having a structure represented by the following formula: 
wherein R4 and R5 are -H or -CH3, R6 and R7 are -H, -OH or an alkyl group having 1-20 carbon atoms, and (b) at least one comonomer selected from the group consisting of a maleic anhydride monomer, an acrylate monomer, a methacrylate monomer, a norbomene monomer, a dihydrofuran monomer and a dihydropyran monomer.
Preferably, at least one of R6 and R7 is selected from a group consisting of alkyl, hydroxyalkyl, alkyloxy, carboxyl, carbonyl, ester and fluorinated alkyloxy.
The comonomer unit is preferably a dihydrofuran or dihydropyran monomer unit. Here, the photosensitive polymer has a structure represented by the following formula: 
wherein r is 1 or 2, R11 and R12 are -H or -CH3, R11 and Rl4 are -H, -OH or an alkyl group having 1-30 carbon atoms and R6, R7, R13 or R14 are an acid-labile group, and m/(m+n+q) is from about 0.1 to 0.8, n/(m+n+q) is in the range of 0.1 to 0.8, and q/(m+n+q) is in the range of 0.1 to 0.8.
In particular, the photosensitive polymer preferably has a structure represented by the following formula: 
wherein R15 is alkyl group having 4-12 carbon atoms and s is an integer of from 0 to 2, preferably 1 to 2. More preferably, R15 is selected from a group consisting of t-butyl, tetrahydropyranyl, and a substituted or unsubstituted alicyclic hydrocarbon group having 6-12 carbon atoms.
Also, the photosensitive polymer preferably has a structure represented by the following formula: 
wherein R15 is an alkyl group having 4-12 carbon atoms and s is an integer of from 0 to 2, preferably 1 to 2.
Further, the photosensitive polymer preferably has a structure represented by the following formula: 
wherein R16 is a C1xcx9cC20 hydrocarbon group. More preferably, R16 is selected from a group consisting of methyl, ethyl, t-butyl and cyclohexyl.
Preferably, the photosensitive polymer has a structure represented by the following formula: 
herein R17 is an alkyl group having 1-20 carbon atoms. More preferably, R17 is selected from a group consisting of methyl, ethyl, t-butyl and cyclohexyl.
In the photosensitive polymer, the comonomer unit preferably has a structure represented by the following formula: 
In particular, the photosensitive polymer preferably has a structure represented by the following formula: 
wherein R8 is an alkyl group having 6-12 carbon atoms and s is an integer of from 0 to 2, preferably 1 to 2. R8 is one of t-butyl, tetrahydropyranyl or a substituted or unsubstituted alicyclic group.
In the case where the comonomer unit is a maleic anhydride monomer unit, the photosensitive polymer preferably has a structure represented by the following formula: 
wherein R11 and R12 are -H or -CH3, R13 and R14 are -H, -OH an alkyl group, at least one of R6, R7, R13 and R14 is an acid-labile group, m/(m+n) is in the range of 0.1 to 0.9, and n/(m+n) is from about 0.1 to 0.9.
In particular, the photosensitive polymer has a structure represented by the following formula: 
wherein R15 is an alkyl group and s is an integer of from 0 to 2. More preferably, R15 is selected from a group consisting of t-butyl, tetrahydropyranyl or a substituted or unsubstituted an alkyl group.
Also, the comonomer unit may include a maleic anhydride monomer unit and an acrylate or methacrylate monomer unit. Here, the photosensitive polymer preferably has a structure represented by the following formula: 
wherein R8 is -H or -CH3, R19 is an acid-labile group, m/(m+n) is in the range of 0.1 to 0.9, and n/(m+n) is in the range of 0.1 to 0.9. More preferably, R19 is one of t-butyl, a tetrahydropyranyl or a substituted or unsubstituted C6xcx9cC12 alicyclic hydrocarbon group.
Also, the comonomer unit may include a maleic anhydride monomer unit and a norbornene monomer unit. Here, the photosensitive polymer preferably has a structure represented by the following formula: 
wherein R20 is an acid-labile group, m/(m+n) is in the range of 0.1 to 0.8, and n/(m+n) is in the range of 0.1 to 0.8. More preferably, R20 is selected from a group consisting of t-butyl, tetrahydropyranyl or a substituted or unsubstituted C6xcx9cC12 alicyclic hydrocarbon group.
The third object of the present invention can be accomplished by providing a resist composition including (a) a photosensitive polymer having a structure represented by the following formula: 
wherein R4 and R5 are -H or -CH3, and R6 and R7 are -H, -OH or an alkyl group having 1-20 carbon atoms and (b) a photoacid generator (PAG). In the resist composition, R6 and R7 is preferably selected from a group consisting of alkyl, hydroxyalkyl, alkyloxy, carboxyl, carbonyl, ester and fluorinated alkyloxy.
Also, in the resist composition, the photosensitive polymer may have various structures as defined above.
According to another aspect of the present invention, there is provided a resist composition including (a) a photosensitive polymer comprising a polymerized product of (i) at least one monomer unit having a structure represented by the following formula: 
wherein R4 and R5 are -H or -CH3, R6 and R7 are -H, -OH or an alkyl group containing 1-20 carbon atoms, and (ii) at least one comonomer selected from the group consisting of a maleic anhydride monomer, an acrylate or methacrylate monomer, a norbomene monomer, and dihydrofuran or dihydropyran monomer, and (b) a PAG.
In the resist composition, the photosensitive polymer may have various structures as defined above.
In the resist composition, the weight average molecular weight of the photosensitive polymer is preferably 3,000xcx9c100,000.
The amount of the PAG may 1xcx9c30 wt % on the basis of the weight of the photosensitive polymer. Preferably, the PAG includes triarylsulfonium salts, diaryliodonium salts, sulfonates, or mixtures thereof. More preferably, the PAG includes triphenylsulfonium triflate, triphenylsulfonium antimonate, diphenyliodonium triflate, diphenyliodonium antimonate, methoxydiphenyliodonium triflate, di-t-butyldiphenyliodonium triflate, 2,6-dinitrobenzyl sulfonates, pyrogallol tris(alkylsulfonates), N-hydroxysuccinimide triflate, norbomene-dicarboximide-triflate, triphenylsulfonium nonaflate, diphenyliodonium nonaflate, methoxydiphenyliodonium nonaflate, di-t-butyldiphenyliodonium nonaflate, N-hydroxysuccinimide nonaflate, norbomene-dicarboximide-nonaflate, PFOS (triphenylsulfonium perfluorooctanesulfonate), diphenyliodonium PFOS, methoxydiphenyliodonium PFOS, di-t-butyldiphenyliodonium triflate, N-hydroxysuccinimide PFOS, norbomene-dicarboximide PFOS, or mixtures thereof. In particular, the resist composition according to the above described aspects of the present invention may further include an organic base. The amount of the organic base is preferably 0.01xcx9c2.0 wt % on the basis of the weight of the photosensitive polymer. Preferably, the organic base includes a tertiary amine compound alone or a mixture of at least two tertiary amine compounds. Examples of the organic base include triethylamine, triisobutylamine, triisooctylamine, triisodecylamine, diethanolamine, triethanolamine, N-alkyl substituted pyrrolidinone, N-alkyl substituted caprolactam, N-alkyl substituted valerolactam, or a mixture thereof. The resist composition according to the above described aspects of the present invention may further include a surfactant of 30 to 200 ppm.
The photosensitive polymer according to the present invention has a structure that has enhanced resistance to dry etching and good adhesiveness to underlying layers. Also, since the photosensitive polymer according to the present invention can be obtained through cationic polymerization, a multi-ring backbone structure can be provided without contamination due to a heavy metal catalyst. Further, the photosensitive polymer included in a resist composition according to the present invention can be adopted to various light sources including KrF excimer lasers (248 nm), ArF excimer lasers (193 nm) or F2 excimer lasers (157 nm). In particular, the resist composition obtained from the photosensitive polymer according to the present invention exhibits superior transmittance at 157 nm. The resist composition has enhanced resistance to dry etching and good transmittance, thereby providing a good lithographic property of high resolution.